Methods, apparatuses and substrate assembly structures for fabricating microelectronic components using mechanical and chemical-mechanical planarization processes

ABSTRACT

Methods, apparatuses and substrate assembly structures for mechanical and chemical-mechanical planarizing processes used in the manufacturing microelectronic-device substrate assemblies. One aspect of the invention is directed toward a method for planarizing a microelectronic-device substrate assembly by removing material from a surface of the substrate assembly, detecting a first change in drag force between the substrate assembly and a polishing pad indicating that the substrate surface is planar, and identifying a second change in drag force between the substrate assembly and the polishing pad indicating that the planar substrate surface is at the endpoint elevation. After the second change in drag force is identified, the planarization process is stopped. The first change in drag force between the substrate assembly and the planarizing medium is preferably detected by measuring a first change in the electrical current through a drive motor driving a substrate holder carrying the substrate assembly and/or a table carrying the polishing pad. The second change in drag force between the substrate assembly and the polishing pad may be identified by detecting a second change in the drive motor current or measuring a second change in the temperature of the planarizing solution or the polishing pad.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of pending U.S. patent application Ser.No. 09/789,352, filed Feb. 20, 2001, which is a divisional of U.S.patent application Ser. No. 09/146,949, filed Sep. 3, 1998, now U.S.Pat. No. 6,191,037.

TECHNICAL FIELD

The present invention relates to fabricating components ofmicroelectronic devices using mechanical and/or chemical-mechanicalplanarizing processes. More specifically, the present invention relatesto methods, apparatuses and substrate assembly structures foridentifying the endpoint in mechanical and/or chemical-mechanicalplanarization of microelectronic substrate assemblies

BACKGROUND OF THE INVENTION

Mechanical and chemical-mechanical planarizing processes (collectively“CMP”) are used in the manufacturing of microelectronic devices forforming a flat surface on semiconductor wafers, field emission displaysand many other microelectronic substrates FIG. 1 schematicallyillustrates a planarizing machine 10 with a platen or table 20, acarrier assembly 30 over the table 20, a polishing pad 40 on the table20, and a planarizing fluid 44 on the polishing pad 40. The planarizingmachine 10 may also have an under-pad 25 between the platen 20 and thepolishing pad 40. In many planarizing machines, a drive assembly 26rotates (arrow A) and/or reciprocates (arrow B) the platen 20 to movethe polishing pad 40 during planarization.

The carrier assembly 30 controls and protects a substrate 12 duringplanarization. The carrier assembly 30 typically has a substrate holder32 that holds the substrate 12 via suction, and a pad 34 in thesubstrate holder 32 that supports the backside of the substrate 12. Adrive assembly 36 of the carrier assembly 30 typically rotates and/ortranslates the substrate holder 32 (arrows C₁ and D, respectively). Thesubstrate holder 32, however, may be a weighted, free-floating disk (notshown) that slides over the polishing pad 40.

The combination of the polishing pad 40 and the planarizing fluid 44generally define a planarizing medium that mechanically and/orchemically-mechanically removes material from the surface of thesubstrate 12. The polishing pad 40 can be a conventional non-abrasivepolishing pad without abrasive particles composed of a polymericmaterial (e.g., polyurethane), or it can be an abrasive polishing padwith abrasive particles fixedly bonded to a suspension material. In atypical application, the planarizing fluid 44 may be a CMP slurry withabrasive particles and chemicals for use with a conventional nonabrasivepolishing pad. In other applications for use with an abrasive polishingpad, the planarizing fluid 44 is generally a “clean” chemical solutionwithout abrasive particles.

To planarize the substrate 12 with the planarizing machine 10, thecarrier assembly 30 presses the substrate 12 against a planarizingsurface 42 of the polishing pad 40 in the presence of the planarizingfluid 44 (arrow C₂). The platen 20 and/or the substrate holder 32 thenmove relative to one another to translate the substrate 12 across theplanarizing surface 42. As a result, the abrasive particles and/or thechemicals in the planarizing medium remove material from the surface ofthe substrate 12.

CMP processes should consistently and accurately produce a uniformlyplanar surface on the substrate assembly to enable precise fabricationof circuits and photo-patterns. During the fabrication of transistors,contacts, interconnects, and other components, many substrate assembliesdevelop large “step heights” that create a highly topographic substratesurface. To enable the fabrication of integrated circuits with highdensities of components, it is necessary to produce a planar substratesurface at several stages of processing the substrate assembly becausenon-planar substrate surfaces significantly increase the difficulty offorming sub-micron features or photo-patterns to within a tolerance ofapproximately 0.1 μm. Thus, CMP processes should typically transform ahighly topographical substrate surface into a highly uniform, planarsubstrate surface (e.g., a “blanket surface”).

In the competitive semiconductor industry, it is also highly desirableto maximize the yield of operable devices as quickly as possible. Onefactor of CMP processing that affects the yield of operable devices isthe ability to accurately stop CMP processing at a desired endpoint. Ina typical CMP process, the desired endpoint is reached when the surfaceof the substrate is highly planar and/or when enough material has beenremoved from the substrate assembly to form discrete components of theintegrated circuits (e.g., shallow-trench-isolation structures,contacts, damascene lines, etc.). Accurately endpointing CMP processingis important for maintaining a high yield because: (1) subsequentprocessing may not be possible if the surface is not sufficientlyplanar; and/or (2) the integrated circuits may not operate if thediscrete components are not accurately formed. For example, if thesubstrate is “under-planarized,” shallow-trench-isolation structures maynot be adequately isolated from one another. Conversely, if thesubstrate assembly is “over-polished,” “dishing” can occur inshallow-trench-isolation structures that can cause current-leakage pathsor parasitic capacitance. Extreme cases of over-polishing can evendestroy sections of the substrate assembly. Thus, it is highly desirableto stop CMP processing at the desired endpoint.

One drawback of CMP processing is that it is difficult to determine whenthe substrate surface is both planar and at the desired endpointelevation in the substrate assembly. In one conventional method fordetermining the endpoint of CMP processing, the planarizing period ofone substrate assembly in a run is estimated using the polishing rate ofprevious substrate assemblies in the run and the thickness of materialthat is to be removed from the particular substrate assembly. Theestimated planarizing period for the particular substrate assembly,however, may not be accurate because the polishing rate may change fromone substrate assembly to another. Thus, this method may not accuratelyplanarize all of the substrate assemblies in a run to the desiredendpoint.

In another method for determining the endpoint of CMP processing, thesubstrate assembly is removed from the pad and the substrate carrier,and then a measuring device measures a change in thickness of thesubstrate assembly. Removing the substrate assembly from the pad andsubstrate carrier, however, is time-consuming and may damage thesubstrate assembly. Thus, this method generally reduces the throughputand yield of CMP processing.

In still another method for determining the endpoint of CMP processing,a portion of the substrate assembly is moved beyond the edge of the pad,and an interferometer directs a beam of light directly onto the exposedportion of the substrate assembly to measure a change in thickness of atransparent layer. The substrate assembly, however may not be in thesame reference position each time it overhangs the pad. For example,because the edge of the pad is compressible, the substrate assembly maynot be at the same elevation for each measurement. Thus, this method mayinaccurately measure the change in thickness of the substrate assembly.

In yet another method for determining the endpoint of CMP processing,U.S. Pat. Nos. 5,036,015 and 5,069,002, which are herein incorporated byreference, disclose detecting the planar endpoint by sensing a change infriction between a wafer and the polishing medium. Such a change offriction may be produced by a different coefficient of friction at thewafer surface as one material (e.g., an oxide) is removed from the waferto expose another material (e.g., a metal film). More specifically, U.S.Pat. Nos. 5,036,015 and 5,069,002 disclose detecting the change infriction by measuring the change in electrical current through the drivemotor for the platen and/or substrate holder.

Although the endpoint detection technique disclosed in U.S. Pat. Nos.5,036,015 and 5,069,002 is an improvement over the previous endpointingmethods, the increase in current through the drive motors may notaccurately indicate the endpoint of a substrate. The detection of asingle change in friction at the interface between the differentmaterials may only indicate that at least a portion of the substratesurface is at the level of the interface. Other portions of thesubstrate surface, however, may be above or below the interface leveland/or the interface level itself may not be planar. The apparatus andmethods disclosed in U.S. Pat. Nos. 5,036,015 and 5,069,002 mayaccordingly indicate that at least a portion of the substrate surface isat the endpoint elevation, but they do not necessarily indicate that thesubstrate surface is planar. Thus, the apparatus and methods of U.S.Pat. Nos. 5,036,015 and 5,069,002 may not indicate that the substratesurface is both planar and at the endpoint elevation.

SUMMARY OF THE INVENTION

The present invention relates to mechanical and chemical-mechanicalplanarizing processes for manufacturing microelectronic-device substrateassemblies. One aspect of the invention is directed toward a method forplanarizing a microelectronic-device substrate assembly by removingmaterial from a surface of the substrate assembly, detecting a firstchange in drag force between the substrate assembly and a polishing padindicating that the substrate surface is at least substantially planar,and identifying a second change in drag force between the substrateassembly and the polishing pad indicating that the planar substratesurface is at least substantially at the endpoint elevation. After thesecond change in drag force is identified, the planarization process isstopped.

The removal of material from the substrate surface generally involvespressing the substrate surface against a polishing pad and impartingrelative motion between the substrate surface and the polishing pad. Thefirst change in drag force between the substrate assembly and thepolishing pad is preferably detected by measuring a first change in theelectrical current through a drive motor driving a substrate holdercarrying the substrate assembly and/or a table carrying the polishingpad. The first change in drag force may alternatively be detected bymeasuring a first change in temperature of the planarizing solution orthe polishing pad. The second change in drag force between the substrateassembly and the polishing pad may be identified by detecting a secondchange in the drive motor current, or measuring a second in thetemperature of the planarizing solution or the polishing pad. The firstchange in drag force indicates that the substrate surface is at leastsubstantially planar, and the second change in drag force indicates thatthe planar substrate surface is at least substantially at the endpointelevation. After the second change in drag force between the substrateassembly and the polishing pad is identified, the act of stoppingremoval of material from the substrate surface generally involvesremoving the substrate assembly from the polishing pad and/orterminating the relative motion between the substrate assembly and thepolishing pad.

In one particular aspect of the invention, the second change in dragforce between the substrate assembly and the planarizing medium isaccentuated from the drag force when the substrate surface is planar byconstructing a substrate assembly including an endpoint indicator havinga first coefficient of friction at an endpoint elevation and a coverlayer having a second coefficient of friction over the endpointindicator. For example, the endpoint indicator is preferably fabricatedby plasma deposition of a silicon nitride layer at the endpointelevation, and the cover layer is preferably formed by depositing a highdensity plasma oxide layer over the plasma silicon nitride layer.Alternatively, the endpoint indicator can be fabricated by depositingeither a silicon carbide layer or a boron nitride layer at the endpointelevation.

In each of these more particular aspects of the invention, the firstchange in drag force can be detected by measuring an increase in theelectrical current through the drive motor of the table from a startcurrent to a planarity current indicating that the substrate surface isplanar and located in the high density plasma oxide layer. Additionally,the second change in drag force can be identified by measuring adecrease in the electrical current through the drive motor from theplanarity current to an endpoint current because each of the plasmasilicon nitride, boron nitride and silicon carbide endpoint indicatorshas a significantly lower coefficient of friction than the high densityplasma oxide layer. Accordingly, many aspects of the invention involvefirst detecting that a planar surface has been formed on the substrateassembly by detecting a first change in the table current, and thenidentifying that the particular endpoint of the substrate assembly hasbeen reached by subsequently identifying a second change in the tablecurrent. Other aspects of the invention also involve modifying thesurface of the endpoint indicator to accentuate the difference in dragforce between the substrate assembly and the polishing pad at theendpoint elevation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view partially illustrating aplanarizing machine in accordance with the prior art.

FIG. 2 is a partial schematic cross-sectional view of one stage in amethod for constructing a shallow-trench-isolation structure on amicroelectronic-device substrate assembly in accordance with oneembodiment of the invention.

FIG. 3 is a partial schematic cross-sectional view of a subsequent stageof the method for constructing shallow-trench-isolation structures shownin FIG. 2.

FIG. 4 is a partial schematic cross-sectional view of a subsequent stageof the method for constructing shallow-trench-isolation structures shownin FIGS. 2 and 3.

FIG. 5A is a partial schematic cross-sectional view of anothersubsequent stage of the method for constructing shallow-trench-isolationstructures shown in FIGS. 2-4.

FIG. 5B is a partial schematic cross-sectional view of anothersubsequent stage of the method for constructing shallow-trench-isolationstructures shown in of FIGS. 2-5A.

FIG. 5C is a diagram illustrating an embodiment of a method forendpointing planarization of a microelectronic-device substrate assemblyby detecting a first change in drag force between the substrate assemblyand the polishing pad, and then identifying a second change in dragforce between the substrate assembly and the polishing pad.

FIG. 6 is a partial schematic cross-sectional view of another subsequentstage of the method for constructing shallow-trench-isolation structuresshown in FIGS. 2-5B.

FIG. 7 is a partial schematic cross-sectional view of another subsequentstage of the method for constructing shallow-trench-isolation structuresshown in FIGS. 2-6.

FIG. 8 is a diagram illustrating another embodiment for endpointingplanarization of a microelectronic-device substrate assembly.

FIG. 9 is a schematic cross-sectional view of a planarizing machine inaccordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present disclosure describes substrate assembly structures,apparatuses and methods for mechanical and/or chemical-mechanicalplanarization of microelectronic-device substrate assemblies. Manyspecific details of certain embodiments of the invention are set forthin the following description, and in FIGS. 2-9, to provide a thoroughunderstanding of the embodiments described herein. One skilled in theart, however, will understand that the present invention may haveadditional embodiments, or that the invention may be practiced withoutseveral of the details described in the following description. Forexample, even though many aspects of the present invention are describedbelow in the context of constructing shallow-trench-isolation (STI)structures, the invention is also applicable to constructing otherstructures and components in the manufacturing of microelectronicdevices.

FIG. 2 is a partial schematic cross-sectional view of one stage in amethod for constructing an STI structure on a microelectronic-devicesubstrate assembly 100 in accordance with one embodiment of theinvention. The substrate assembly 100 has a substrate 110, a thin oxidelayer 120 formed over the substrate 110, and an elevation indicator orendpoint indicator 130 formed over the oxide layer 120. In thefabrication of STI structures and other components for integratedcircuits in semiconductor devices, the substrate 110 is preferably asingle crystal silicon wafer. The substrate 110 can alternatively be aglass substrate for a baseplate of a field emission display, or anyother suitable type of substrate for other types of microelectronicdevices. When the substrate 110 is composed of silicon, the oxide layer120 is preferably a thin layer of silicon dioxide grown by oxidizing thesurface of the substrate 110. The oxide layer 120, for example,generally has a thickness of approximately 100 Å to define a pad oxidelayer.

The endpoint indicator 130 is fabricated on the oxide layer 120 so thata top surface 132 of the endpoint indicator 130 is located at a desiredendpoint elevation for subsequent CMP processing of the substrateassembly 100. The endpoint indicator 130 is composed of a material thathas a first coefficient of friction, such as a material having either avery high or a very low coefficient of friction. For example, lowfrictional coefficient endpoint indicators can be composed of siliconcarbide, boron nitride, or plasma deposited silicon nitride. Suitabledeposition techniques for the plasma deposited silicon nitride includeplasma vapor deposition techniques that are known in the semiconductordevice fabrication arts. After the endpoint indicator 130 has beenformed, the trenches for the STI structures are formed.

FIGS. 3 and 4 are partial schematic cross-sectional views of subsequentstages of the method for constructing an STI structure on the substrateassembly 100. FIG. 3 illustrates the substrate assembly 100 after aplurality of trenches 112 have been etched in the substrate 110 and anoxide liner 122 has been grown in each of the trenches 112. The trenches112 are formed by photo patterning a layer of resist (not shown) on theendpoint indicator 130, and then etching through the endpoint indicator130, the oxide layer 120, and a portion of the substrate 110. The oxideliner 122 is then formed by oxidizing the exposed silicon in thetrenches 112 to grow a thin layer of silicon dioxide in the trenchesthat connects with the silicon dioxide of the oxide layer 120. Isolatedpads of the endpoint indicator 130 are then left on the oxide layer 120between the trenches 112.

Referring to FIG. 4, the material for the STI structures is provided bydepositing a cover layer 124 over the endpoint indicator 130 and intothe trenches 112. The cover layer 124 has a second coefficient offriction that is different from the first coefficient of friction of theendpoint indicators 130. For example, when the cover has a relativelyhigh coefficient of friction, the endpoint indicator 130 is selectedfrom a material having a low coefficient of friction. Alternatively, thetop surfaces 132 of the endpoint indicator 130 can be treated to imparta high or low coefficient of friction to the endpoint indicator 130. Thecover layer 124 is preferably formed by depositing silicon dioxide usinga high density plasma process. The high density plasma (HDP) silicondioxide combines with the silicon dioxide liner 122 (FIG. 3) and theoxide layer 120 to form an integral cover layer 124 of silicon dioxide.The HDP silicon dioxide has a higher coefficient of friction than boronnitride, silicon carbide, or plasma deposited silicon nitride used asthe endpoint indicator 130. At this point of fabricating the STIstructures, the substrate assembly 100 is now ready to be planarized toremove excess material of the cover layer 124 from the substrateassembly 100.

FIGS. 5A and 5B are partial schematic cross-sectional views illustratingsubsequent stages of the method for constructing an STI structureinvolving mechanical and/or chemical-mechanical planarization of thesubstrate assembly 100. Referring to FIG. 5A, the substrate assembly 100is inverted and attached to a backing pad 34 in a substrate holder 32 sothat the substrate assembly 100 is positioned over a polishing pad 40 ona table 20. The table 20, substrate holder 32, backing pad 34, andpolishing pad 40 can be similar to those described above with respect toFIG. 1. The substrate holder 32 then presses the cover layer 124 againstthe polishing pad 40, and the substrate holder 32 and/or the polishingpad 40 move to translate the substrate assembly 100 across the polishingpad 40 in the presence of a planarizing solution (not shown). After aperiod of time, a planar substrate surface 127 is formed at anintermediate elevation in the cover layer 124. The substrate surface127, more particularly, becomes planar at an elevation spaced apart fromthe top surfaces 132 of the endpoint indicators 130.

Referring to FIG. 5B, the substrate assembly 100 is further planarizeduntil the substrate surface 127 of the cover layer 124 is coplanar withexposed top surfaces 132 of the endpoint indicators 130. At this pointof the planarizing stage, it is important to accurately stop removingmaterial from both the endpoint indicators 130 and the cover layer 124to prevent over-polishing or under-polishing of the substrate assembly100.

FIG. 5C illustrates one embodiment for accurately endpointing theplanarizing stage of the method for forming STI structures. The endpointis determined by detecting a first change in drag force between thesubstrate assembly and the polishing pad indicating that the substratesurface 127 has become planar (FIG. 5A), and then identifying a secondchange in drag force caused by exposing the endpoint indicators 130indicating that the planar substrate surface 127 is at the endpointelevation (FIG. 5B). FIG. 5C, more particularly, illustrates anembodiment of the method in which: (1) the first and second changes indrag force are indicated by measuring a change in the electrical currentthrough a drive motor driving the table 20 (FIG. 1) of the planarizingmachine; and (2) the second coefficient of friction of the cover layer124 is greater than the first coefficient of friction of the endpointindicators 130. The resulting current trace exhibits a start up current140, a first change in current 142 detecting the first change in dragforce, a planarity current 146, and a second change in current 148identifying a second change in drag force.

Still referring to FIG. 5C, the start up current 140 remains relativelyconstant during a first stage A of the CMP process because the coverlayer 124 is highly topographical (FIG. 4) and the surface area of thesubstrate assembly 100 contacting the polishing pad 40 remainsrelatively constant. The first change in current 142 increases rapidlyin a second stage B of the CMP process because, as the substrate surface127 becomes planar (FIG. 5B), the increase in surface area of thesubstrate assembly 100 contacting the polishing pad significantlyincreases the drag force between the substrate assembly 100 and the pad.Once the substrate surface 127 becomes planar, the table current remainssubstantially constant at the planarity current 146 in a third stage Cof the CMP process. The second change in current 148 then decreasesrapidly during a fourth stage D of the CMP process as the top surfaces132 of the endpoint indicators 132 are exposed because the lowercoefficient of friction of the endpoint indicators 130 reduces the dragforce between the substrate assembly 100 and the polishing pad 40. Theplanarizing process is terminated after the second change 148 in currentoccurs indicating that the top surfaces 132 of the endpoint indicators130 are exposed across the face of the substrate assembly 110 (FIG. 5B).

FIGS. 6 and 7 are partial schematic cross-sectional views illustratingsubsequent processing of the substrate assembly 100 after the substrateassembly 100 has been planarized to form the STI structures. Referringto FIG. 6, the substrate assembly 100 is dipped in a buffered HFsolution to remove a portion of the cover layer 124 between the endpointindicators 130. The upper surfaces 127 of the cover layer 124 areaccordingly slightly below the exposed surfaces 132 of the endpointindicators 130.

FIG. 7 illustrates the substrate assembly 100 after the endpointindicators 130 have been removed and the cover layer 124 (FIG. 6) hasbeen uniformly etched to form a plurality of STI structures 128 betweenactive areas 114 of the substrate 110. When the endpoint indicators 130are formed from plasma silicon nitride, the endpoint indicators 130 arestripped from the substrate assembly 100 by dipping the substrateassembly 100 in a phosphoric acid dip. The cover layer 124 is thenetched until the sections of the cover layer 124 that were previouslyunder the endpoint indicators 130 (see FIG. 6) are removed to expose theactive areas 114 of the substrate 110. The STI structures 128 fillingthe trenches 112 in the substrate 110 accordingly isolate active areas114 of the substrate 110 from one another. As such, active features 113can be constructed on the active areas 114 in accordance with knownmicroelectronic-device fabrication processes. During the fabrication ofsuch active features 113 and the associated contacts, the raisedportions of the STI structures 128 are generally lowered toapproximately the level of the substrate 110 (not shown)

The methods set forth above with respect to FIGS. 2-7 enhance the yieldof operable STI structures because the process for endpointing theplanarizing stage accurately indicates both the planarity and theendpoint elevation of the substrate surface. Conventional planarizingand endpointing methods often produce surfaces with variances from thedesired endpoint elevation of approximately ±200 Å because they do notdetect whether the substrate surface is planar. In contrast toconventional end pointing methods, by first detecting that the substratesurface is planar and then identifying that the substrate surface is atthe endpoint elevation in accordance with the methods set forth abovewith respect to FIGS. 2-7, the deviation in uniformity across thesurface of the substrate assembly is generally approximately ±10 Å.Several embodiment of the end pointing process of the invention are thusexpected to reduce problems associated with over-polishing orunder-polishing the substrate assembly that can create current leakagepaths or even destroy the integrated circuit components on substrateassemblies.

FIG. 8 is a diagram illustrating another embodiment of a process for endpointing the planarizing stage of processing a semiconductor assembly.In this embodiment, the start up current 140, the first change incurrent 142, and the planarity current 146 follow a trace similar tothat described above with respect to FIG. 5C. The endpoint indicators130 (FIGS. 2-5B) of this embodiment, however, have a higher coefficientof friction than the cover layer 124 (FIGS. 2-5B). Accordingly, thesecond change in current 149 increases from the planarity current 146 toan endpoint current at the end of the fourth stage D of the planarizingprocess. The difference in the coefficient of friction between the coverlayer 124 and the endpoint indicators 130 can accordingly be selectedsuch that the second change in drag force after the substrate surface127 has become planar may accordingly increase or decrease with respectto the drag force when the substrate surface is planar.

In another embodiment (not shown), the slurry can be modified orselected to cause a decrease in drag force as the substrate surface 127becomes planar such that the first change in drag force decreases duringthe second stage B (FIG. 5C) of the planarizing process. One suitableslurry for decreasing the drag force as the substrate surface 127becomes planar is Klevesol, manufactured by Rodel Corporation. Thus, thefirst change in the table current may decrease from the start current.

In still another embodiment of the invention, the first and/or secondcoefficients of friction of the endpoint indicator 130 and/or the coverlayer 124 can be modified to increase the difference between the firstand second coefficients of friction. Referring to FIG. 5B for example, aslurry (not shown) between the substrate assembly 100 and the polishingpad 40 can be modified or selected to react with the top surfaces 132 ofthe endpoint indicator 130 in a manner that either reduces or increasesthe first coefficient of friction of the top surfaces 132 of theendpoint indicator 130. One particular embodiment adds surfactantsand/or other chemicals to a slurry to increase or decrease the firstcoefficient of friction of the surface stratum of an endpoint indicator130. For example, a polyoxyethylene ether can be added to a slurry(e.g., Corrundum or ILD-1300 slurries manufactured by Rodel Corporation)to decrease the coefficient of friction at the surface of a siliconnitride endpoint indicator. This particular embodiment is accordinglyparticularly well suited for use with a cover layer composed of silicondioxide because it increases the difference between the coefficients offriction between the reacted silicon nitride and the silicon dioxide.

In another embodiment, the top surfaces 132 of the endpoint indicator130 can be modified using implantation, diffusion, deposition or othertechniques to create a surface stratum of the endpoint indicator 130having a desired coefficient of friction. Referring to FIGS. 2 and 3,for example, the surface of the endpoint indicator 130 can be treated toincrease or decrease the difference in the coefficients of friction atthe interface between the endpoint indicator 130 and the cover layer 124(FIG. 4). One particular embodiment involves implanting boron, phosphorand/or carbon into a silicon nitride endpoint indicator to create asurface stratum having a lower coefficient of friction than theuntreated silicon nitride. Another particular embodiment involvesdiffusing boron and/or phosphor into a polysilicon endpoint indicator tocreate a surface stratum having a different coefficient of friction thanthe polysilicon. Still another particular embodiment involves depositinga thin layer of silicon carbide or boron over a thermally depositedsilicon nitride layer (e.g., Chemical Vapor Deposition) to produce asurface stratum having a lower coefficient of friction than the siliconnitride layer.

FIG. 9 is a schematic cross-sectional view of a planarizing machine 110in accordance with yet another embodiment of the invention in which thefirst and second changes in drag force can be monitored by measuring thetemperature change of the slurry, the polishing pad and/or the substrateassembly. The planarizing machine 110, for example, can have an infraredsensor 170 positioned over the polishing pad to measure the temperaturechanges of either the polishing pad 40 or the planarizing solution 44 onthe polishing pad 40. In alternative embodiments, the planarizingmachine 110 can have a temperature sensor 172 touching the planarizingsolution 44 on the pad 40, or a temperature sensor 174 located in a flowof planarizing solution 44 off of the polishing pad 40. In still anotheralternative embodiment, a temperature sensor 176 attached to thesubstrate holder 32 measures changes in the temperature of the substrateassembly 100. In these embodiments, an increase in temperature indicatesa corresponding increase in drag force between the substrate assembly100 and the polishing pad 40. Similarly, a decrease in temperatureindicates a decrease in drag force. The changes in temperature areexpected to follow traces similar to those shown in FIGS. 5C and 8,except that the axis labeled “Table Current” would represent the“Temperature.”

From the foregoing it will be appreciated that, although specificembodiments of the invention have been described herein for purposes ofillustration, various modifications may be made without deviating fromthe spirit and scope of the invention. Accordingly, the invention is notlimited except as by the appended claims.

What is claimed is:
 1. A method of fabricating a substrate assemblystructure for microelectronic devices comprising: forming an endpointindicator by depositing a layer of silicon nitride at an elevation abovea semiconductor substrate; treating a surface of the endpoint indicatorby implanting at least one of phosphor and carbon to obtain a stratum ofmaterial at an endpoint elevation on the endpoint indicator, the stratumhaving a first coefficient of friction; and depositing a cover layerover the stratum, the cover layer having a second coefficient offriction different from the first coefficient of friction, thedifference between the first coefficient of friction and the secondcoefficient of friction being detectable to indicate the endpointelevation during a planarization process.
 2. The method according toclaim 1 wherein depositing a cover layer further comprises depositing ahigh-density plasma oxide layer over the stratum.
 3. A method offabricating a substrate assembly structure for microelectronic devices,comprising: forming a polysilicon endpoint indicator at an elevationabove a semiconductor substrate; treating a surface of the endpointindicator by diffusing at least one of boron and phosphor into theendpoint indicator to obtain a stratum of material at an endpointelevation on the endpoint indicator, the stratum paving a firstcoefficient of friction; and depositing a cover layer over the stratum,the cover layer having a second coefficient of friction different flowthe first coefficient of friction, the difference between the firstcoefficient of friction and the second coefficient of friction beingdetectable to indicate the endpoint elevation during a planarizationprocess.
 4. The method according to claim 3 wherein depositing a coverlayer further comprises depositing a high-density plasma oxide layerover the stratum.